In a W-CDMA communication system in conformity with 3GPP (3rd Generation Partnership Project), which is caused to become the standard currently, HSDPA (High Speed Downlink Packet Access) is proposed as a technique to achieve a high-speed downlink.
As shown in FIG. 1, a W-CDMA communication system comprises a mobile station and a base station. In the HSDPA, the base station transmits packet data to the mobile station by an HS-PDSCH (High Speed Physical Downlink Shared Channel). Further, before transmitting the packet data by the HS-PDSCH, the base station transmits control information (packet control information) used for demodulation and decoding of the packet data to the mobile station by an HS-SCCH (High Speed Shared Control Channel). The control information (packet control information) includes information on channelization codes (a multicode number indicating the number of channelization codes assigned to one mobile station and a code offset indicating an offset value of a channelization code).
As a characteristic function of the HSDPA, there is a function that the mobile station calculates a status of a propagation path, which changes minute by minute, as an index value of a CQI, maps the calculated CQI on an HS-DPCCH (High Speed Dedicated Physical Control Channel), and regularly transmits it to the base station.
Thus, inasmuch as the base station can grasp the latest status of the propagation path, it is possible to obtain a merit that a transmission rate of the HS-PDSCH can be optimized in a time unit of two milliseconds of the shortest period, which is a subframe. Further, by optimization of the transmission rate of the HS-PDSCH, it is possible to obtain a merit that a channel resource of the HS-PDSCH can be used effectively.
Techniques regarding the CQI are disclosed in various Patent Documents. For example, International Publication No. 2004/077871 pamphlet (hereinafter, referred to as “Patent Document 1”) discloses a base station and a terminal (mobile station) that can achieve reduction of collision of cycle information transmitted from the terminal (mobile station) to the base station, and restrain interference of communication as much as possible. In Patent Document 1, the base station includes a receiving section for receiving quality information (CQI) indicating a current communication state, which is periodically transmitted from the terminal (mobile station) to the base station, and a cycle processing section for calculating and adding a time offset variable with respect to reception timing of the quality information. Further, the terminal (mobile station) includes a transmitting section for transmitting the quality information (CQI), and a cycle processing section for calculating and adding a time offset variable with respect to transmission timing of the quality information.
Patent Document 1 is one that discloses a technical idea to achieve reduction of collision of a CQI (cycle information) regularly transmitted from a mobile station to a base station by shifting transmission/reception timing of the CQI. Therefore, Patent Document 1 fails to disclose control for stopping or starting transmission of the CQI itself, and has no description that suggests it.
Further, Japanese Patent Application Publication No. 2004-134898 (corresponding to U.S. Patent Application Publication No. 2005/0174982) (hereinafter, referred to as “Patent Document 2”) discloses a technical idea to carry out the optimum scheduling according to data of each mobile station in an up line. In Patent Document 2, a mobile station comprises a buffer for storing transmission data, a CQI generating section for generating a CQI according to communication quality, and a transmission control section for controlling a transmission interval for transmitting the CQI in accordance with one of the amount of transmission data stored in the buffer and a value related to the transmission data. A base station comprises a CQI extracting section for extracting a CQI from reception data, an observing section for observing the number of reception slots of the CQI, a scheduler for carrying out scheduling on the basis of the CQI extracted by the CQI extracting section and the number of reception slots in a predetermined period of time, and a data generating section for generating transmission data with scheduling in this scheduler.
This Patent Document 2 discloses a technical idea to control a transmission interval for transmitting the CQI in accordance with the amount of transmission data stored in the buffer. However, in Patent Document 2, it is not considered whether or not the base station carries out transmission to the mobile station when the transmission interval of the CQI is controlled.
Japanese Patent Application Publication No. 2004-147050 (corresponding to U.S. Patent Application Publication No. 2004/0127221) (hereinafter, referred to as “Patent Document 3”) discloses a mobile communication system capable of reducing delay of packet transmission effectively. In Patent Document 3, the mobile communication system comprises a base station and a mobile station. A radio link is set up between the base station and the mobile station. A packet is transmitted from the base station to the mobile station using the radio link. The base station comprises a base station transmitting and receiving section for setting up a radio link in the mobile station, a base station state updating section for generating transmission and reception state updating information indicating a packet receivable state in the mobile station and for notifying this transmission and reception state updating information to the base station, and a base station memory section for continuously holding individual physical channel setting information in the radio link at a suspended state. The mobile station comprises a mobile station transmitting and receiving section for setting up a radio link in the base station, a mobile station state updating section for setting up one of an active state in which reception of a packet is possible and a suspended state in which reception of a packet is impossible on the basis of transmission and reception state updating information, and a base station memory section for continuously holding individual physical channel setting information in the radio link at the suspended state.
Patent Document 3 merely discloses a technical idea to notify the transmission and reception state updating information from the base station to the mobile station using the HS-SCCH (High Speed Shared Control Channel). Patent Document 3 fails to disclose a technique to control a transmission cycle of a CQI, and has no description that suggests it.
The transmission cycle of the CQI is defined in TS25.331 of 3GPP. According to the TS25.331, the base station specifies any of 0, 2, 4, 8, 10, 20, 40, 80 and 160 (unit is milliseconds) as a transmission cycle of a CQI against the mobile station before starting communication of HSDPA.
Generally, the base station makes a transmission cycle longer in the case where it is determined that a propagation path status at this time is stable. It makes the transmission cycle shorter in the case where it is determined that it is unstable. Further, once this transmission cycle is set up in the mobile station, it is used until it is reset up. In the case where it is to be reset up, it is necessary to carry out a setting process using an upper layer against the mobile station.
Now, as shown in FIG. 1, in the base station, there is a period when transmission of packet data by the HS-PDSCH is not carried out. In FIG. 1, subframes shown with half-tone dot meshing indicate that the base station does not carry out transmission by the HS-SCCH and the HS-PDSCH for the mobile station.
However, inasmuch as the transmission cycle of the CQI is regular as described above (in FIG. 1, two milliseconds), there is possibility that the mobile station continues transmission of the HS-DPCCH in which the CQI is mapped even in a period when the base station does not carry out transmission of the HS-PDSCH.
Inasmuch as the transmission of the CQI is unnecessary except for the time when packet data are received by the HS-PDSCH, transmission of the CQI mapped on the HS-DPCCH except for the time when packet data are received by the HS-PDSCH becomes a long process. The longer a period when transmission of packet data by the HS-PDSCH from the base station is not carried out is, the more remarkable this long process becomes.
On the other hand, Japanese Patent Application Publication No. 2003-199173 (corresponding to U.S. Pat. No. 6,993,294) (hereinafter, referred to as “Patent Document 4”) discloses a mobile communication system that can reduce power consumption of a mobile station, reduce interference wave power of an up line and increase capacity of the up line. In Patent Document 4, a base station sets up an upward control channel with the mobile station to transmit a pilot signal. The mobile station measures reception quality of this pilot signal, and transmits quality information (CQI) to the base station using an upward quality control channel (HS-DPCCH: High Speed-Dedicated Physical Control Channel). The base station carries out transmission control of data to the mobile station using this quality information (CQI). The mobile station is set up so as to carry out transmission start and stop control of the quality information, and the quality information is transmitted only if needed.
Patent Document 4 discloses a technical idea to control transmission of the quality information (CQI) from the mobile station to the base station only if needed. In order to achieve this, transmission start and stop control of the quality information (CQI) are carried out during setting of the upward quality control channel (HS-DPCCH) in the mobile station. To be explained in detail, in Patent Document 4, in order to stop transmission of the quality information (CQI), the base station carries out notification of termination of data transmission to the mobile station using an individual channel DL DPCH (Dedicated Physical Channel), the mobile station determines whether final packet data are received or not, or the base station determines whether off of a Request Indicator to be transmitted is received for the predetermined number of times or not. In any case, in Patent Document 4, it is required to use the individual channel, or carry out complicated determination in the mobile station.